The current trend in design of electrohydraulic systems, particularly systems for use in mobile applications such as construction equipment, is toward the use of electrohydraulic pilot valves that operate the main system control valve. In systems of this type, an electrical signal from a controller, which may be an operator controller and/or a microprocessor-based automated controller, is supplied to the pilot valve. The output from the pilot valve is in the form of hydraulic fluid pressure that is proportional to the input control signal. This output pressure may be connected to the control ports of a hydraulic load, such as a hydraulic control valve. The electrohydraulic pilot valve may be provided in the form of a stand-alone valve disposed remotely of the load and connected thereto by suitable fluid lines, or may be incorporated into or mounted on the housing of the hydraulic load.
Conventional electrohydraulic pilot valves typically include a spool movably mounted within a valve body for variably coupling the valve inlet to the valve outlet. An electrical solenoid is mounted on or within the valve body, and is responsive to the electrical control signals for applying a variable pressure to one end of the spool. Valve outlet pressure is fed back to the opposing end of the spool. This pressure acts on the effective area of the spool, creating a force opposing the solenoid. Pilot valve outlet pressure is therefore a function of the input force applied by the solenoid, which in turn is a function of magnitude of the control signal applied to the solenoid.
There is a desire and need in the art for pilot valves of the described character that are capable of supplying increased pilot output pressure while maintaining or reducing electrical power consumption. Output pressure is a function of spool diameter and solenoid force. In order to boost output pressure in conventional valve constructions, either the spool area must be reduced or the solenoid output force must be increased. Increased solenoid force typically necessitates increased electrical power consumption, which in turn implies increased costs and is therefore not desirable. On the other hand, decreasing spool diameter would increase manufacturing cost, and would also deleteriously affect dynamic performance characteristics because of the consequent reduction in flow area.
It is therefore a general object of the present invention to provide an electrohydraulic system, and particularly an electrohydraulic pilot valve system, that obtains increased fluid outlet pressure while maintaining or reducing electrical power consumption. A further object of the present invention is to provide an electrohydraulic valve of the described character that obtains the foregoing objective without significant increase in manufacturing costs, and while maintaining or improving dynamic performance characteristics of the valve.